Electron gun assemblies



May 8, 1962 D. B. GAssoN 3,034,012

ELECTRON GUN AssEMBLIEs Filed oct. 14. 1959 477-0 PNE Y United LtatesThis invention relates to electron gun assemblies particularly wherelarge beam currents, of the order of 250 milliarnps or more, arerequired. The invention has applcation in the use of focused electronbeams to produce intense localised heating of a bombared object.

According to the present invention an electron gun assembly comprises ametal member having a slit, a ilamentary cathode wire extendinglongitudinally of the slit, and means for moving said wire into and outof the slit transversely to the surface of the member to control themagnitude of the electron emission.

The cathode wire may extend between two posts each supported so as to beslidable in a direction extending transversely of the surface of themember. The posts may be mounted in holes in a block secured to saidmem- Iber.

In order that the invention may -be more fully understood reference willnow be made to the drawing accompanying this specilication, in which:

FIG. 1 shows one embodiment of the invention in section; and

-FlG. 2 shows a view of the cathode unit.

Referring now to FIG. 1 there is shown therein an electron gun assemblycomprising a cathode unit formed by a metal block l having lateral ns tofacilitate cooling by air blast and which is capped by a metal member 2in the form of a disc having a slit 3 in which is positioned a lamentarycathode wire 4 extending longitudinally of the slit. In FIG. 2 thecathode wire 4 and slit 3 are shown more clearly. Block 1 can beconstructed of brass and member 2 of copper. While block l isillustrated as being finned to facilitate air blast cooling, any othermethod of cooling could equally well be used, bearing in mind that thestructure is at a high potential relative to earth.

In order to control the magntiude of the electron emission from cathodewire 4 means are provided for moving the Wire into and out of the slittransversely to the surface of copper disc 2. To achieve this thecathode wire is arranged to extend between two posts 5 and 6 which aremounted in holes in block 1 so as to be slidable in a directionextending transversely to the surface of member 2. The filament heatercurrent is passed between the posts and they are each electricallyinsulated from block 1 by means of recessed 0 rings 7 and S which serveas spacers and vacuum seals. Rings 7 and 8 can conveniently be formed ofneoprene The space above atent the rings may be oil-filled. Nuts 9 and10 constructed of an insulating material such as Tufnol are screwedon toscrew threads provided on the posts and are a sliding lit incounter-bores provided in block 1. The posts 5 and 6 are held relativeto each other 'oy means of an insulating cross piece ll and the nuts 9and 10. Cross piece ll can be formed from Bakelite. The posts may bemoved axially by rotation of an insulated screw 1'2 which is threadedthrough cross head ll and bears against the top of modulator block l.Maximum electron current is obtained when filament 4 is positioned wellforward in slit 3 and rotation of screw l2 to withdraw the lilament intothe disc reduces the beam current.

The assembly also includes a metal accelerating anode i3 positioned soas not to intercept any part of the electron beam, a Ibeam focusing coili4 and beam deflecting coils 15. The anode structure is closely spacedfrom the cathode unit but is held insulated therefrom by means of aglass cylinder f6. lt will be appreciated that the guns would beoperated in a vacuum enclosure.

One advantage of such an electron gun assembly is that where more thanone gun is used from the same power supply independent beam currentcontrol can be elfected by controlling the position of the cathode wireof each assembly without necessity for the adjustment of the filamentcurrent or the anode voltage of individual guns. Furthermore it is notnecessary to match the lilament of each gun in the event of failure ofone of them.

What l claim is:

l. An electron gun assembly comprising a hollow block, a metallic memberhaving a slit capping one end of the block, a pair of posts extendingwithin said block, a iilamentary cathode wire extending between saidposts longitudinally of said slit, means for moving said posts in unisonin a direction perpendicular to the surface of said metallic member soas to cause said wire to move into and out of said slit, whereby tocontrol the electron emission, and external electrical connections tosaid posts to enable heating current to be passed through said wire.

2. An electron gun assembly comprising a hollow block, a metallic memberhaving a slit capping one end of the block, a pair of posts extendingwithin said block perpendicularly to the surface of said metallicmember, a lilamentary cathode wire detachably secured between said postsand extending longitudinally of said slit, meansfor moving said postsaxially in unison so as to cause said wire to move into and out of saidslit, whereby to control the electron emission, and external electricalconnections to said posts to enable heating current to be passed throughsaid wire.

Hillier Dec. 25, 1945 Poittevin May 20, 1952

